1. Field of the Invention
The present invention relates to flux mapping systems for nuclear reactors and, more particularly, to increasing drivability of detectors in a flux mapping system.
2. Description of the Related Art
Nuclear reactors include incore and excore detectors, i.e., detectors which are positioned inside the nuclear reactor core and detectors which are outside the core but inside the containment. Flux detectors, for example, may be used both inside the core and outside the core. In both cases, the flux detectors measure neutron flux emanating from the fuel in the core. The incore flux detectors are inserted into thimbles which pass through the core. The incore flux detectors are then drawn out of the core at a predetermined rate to produce a flux map along each thimble.
A flux detector distribution system supplies the flux detector to the thimbles in the core of a nuclear reactor. A pressurized water nuclear reactor typically has approximately 60 thimbles, but may have only four detectors. The flux detectors are mounted on the ends of cables which can be wound onto reels in drive units driven by motors. A network of tubing and multiple-path selectors enable any of the detectors from these reels to enter into any of the thimbles. Typically, if the driving force on the detector is 70 pounds when leaving the cable reel, the driving force when entering the thimbles ranges from 11.5 pounds to as little as five pounds.
Previous attempts to increase the driving force at the thimbles included adjusting the clutch mechanism in the cable reel drive to provide more force before the clutch would slip. This inevitably led to cable deformation problems. Another attempted solution was to replace conventional mechanical path verification switches with non-contact path verification switches to reduce friction on the cable. At best this resulted in only a ten percent increase in driving force.